swab(1): comment code

src/swab.rs

@@ -27,15 +27,12 @@ extern crate getopt;
 use getopt::GetOpt;
 
 extern crate sysexits;
-use sysexits::{ EX_OK, EX_OSERR, EX_USAGE };
+use sysexits::{ EX_IOERR, EX_OK, EX_USAGE };
 
 extern crate strerror;
 use strerror::StrError;
 
-fn oserr(s: &str, e: Error) -> ExitCode {
-	eprintln!("{}: {}", s, e.strerror());
-	ExitCode::from(EX_OSERR as u8)
-}
+fn err(s: &str, e: Error) { eprintln!("{}: {}", s, e.strerror()); }
 
 fn usage(s: &str) -> ExitCode {
 	eprintln!("Usage: {} [-f] [-w word_size]", s);
@@ -44,19 +41,20 @@ fn usage(s: &str) -> ExitCode {
 
 fn main() -> ExitCode {
 	let argv = args().collect::<Vec<String>>();
-	let mut buf: Vec<u8> = Vec::new();
+	let mut buf: Vec<u8> = Vec::new(); // holds the sequence getting swabbed
 	let mut input = stdin();
 	let mut output = stdout().lock();
 
 	let mut force = false;
-	let mut wordsize: usize = 2;
+	let mut wordsize: usize = 2; // default; mimics dd(1p) conv=swab
 
 	while let Some(opt) = argv.getopt("fw:") {
 		match opt.opt() {
 			Ok("f") => force = true,
-			Ok("w") => {
+			Ok("w") => { // sets new sequence length
 				if let Some(arg) = opt.arg() {
 					match arg.parse::<usize>() {
+						// an odd sequence length is nonsensical
 						Ok(w) if w % 2 == 0 => { wordsize = w; () },
 						_ => { return usage(&argv[0]); },
 					}
@@ -70,21 +68,28 @@ fn main() -> ExitCode {
 
 	loop {
 		match input.read(&mut buf) {
-			Ok(0) => break ExitCode::from(EX_OK as u8),
-			Ok(v) if v == wordsize => {
+			Ok(0) => break ExitCode::from(EX_OK as u8), // read nothing; bye
+			Ok(v) if v == wordsize => { // read full block; swab
 				let (left, right) = buf.split_at(v/2);
+
 				if let Err(e) = output.write(&right)
 						.and_then(|_| output.write(&left)) {
-					break oserr(&argv[0], e)
+					err(&argv[0], e);
+					break EX_IOERR // write error
 				}
+
 			},
-			Ok(v) => {
+			Ok(v) => { // partial read; partially write
 				if let Err(e) = output.write(&buf[..v]) {
-					break oserr(&argv[0], e)
+					err(&argv[0], e);
+					break EX_IOERR // write error
 				}
 			},
 			Err(e) if e.kind() == ErrorKind::Interrupted && force => continue,
-			Err(e) => break oserr(&argv[0], e)
+			Err(e) => {
+				err(&argv[0], e);
+				break EX_IOERR // read error (or signal)
+			}
 		}
 	}
 }